Array substrate for in-plane switching mode liquid crytal display device having double-layered metal patterns and method of fabricating the same

ABSTRACT

An array substrate of an in-plane switching liquid crystal display device includes, among other features, a gate electrode and a gate line having a first double-layered structure consisting of a first barrier layer and a first low resistance metallic layer; a data line defining a pixel region with the gate line, the data line having a second double-layered structure consisting of a second barrier layer and a second low resistance metallic layer; a plurality of common electrodes disposed in a direction opposite to an adjacent gate line; a thin film transistor (TFT) near a crossing of the gate and data lines, each of the source and drain electrodes of the TFT having the same double-layered structure as the data line; and a plurality of pixel electrodes arranged in an alternating pattern with the common electrodes and disposed in the direction opposite the adjacent gate line.

This application claims the benefit of Korean Patent Application No.2003-0041166, filed on Jun. 24, 2003, which is hereby incorporated byreference as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to liquid crystal display devices. Moreparticularly, the present invention relates to liquid crystal displaydevices implementing in-plane switching (IPS) where an electric fieldapplied to liquid crystals is generated in a plane parallel to asubstrate.

2. Discussion of the Related Art

A liquid crystal display device uses the optical anisotropy andpolarization properties of liquid crystal molecules to produce an image.Liquid crystal molecules have a definite orientational alignment as aresult of their long, thin shapes. The alignment direction can becontrolled by an applied electric field. In other words, as an appliedelectric field changes, so does the alignment of the liquid crystalmolecules. Due to the optical anisotropy, the refraction of incidentlight depends on the alignment direction of the liquid crystalmolecules. Thus, by properly controlling an applied electric field, adesired light image can be produced.

Of the different types of known liquid crystal displays (LCDs), activematrix LCDs (AM-LCDs), which have thin film transistors (TFTs) and pixelelectrodes arranged in a matrix form, are the subject of significantresearch and development because of their high resolution andsuperiority in displaying moving images.

LCD devices have wide application in office automation (OA) equipmentand video units because they are light and thin and have low powerconsumption characteristics. The typical liquid crystal display panelhas an upper substrate, a lower substrate and a liquid crystal layerinterposed therebetween. The upper substrate, commonly referred to as acolor filter substrate, usually includes a common electrode and colorfilters. The lower substrate, commonly referred to as an arraysubstrate, includes switching elements, such as thin film transistorsand pixel electrodes.

LCD device operation is based on the principle that the alignmentdirection of the liquid crystal molecules is dependent upon an electricfield applied between the common electrode and the pixel electrode.Thus, the alignment direction of the liquid crystal molecules iscontrolled by the application of an electric field to the liquid crystallayer. When the alignment direction of the liquid crystal molecules isproperly adjusted, incident light is refracted along the alignmentdirection to display image data. The liquid crystal molecules functionas an optical modulation element having variable optical characteristicsthat depend upon polarity of the applied voltage.

In a related art LCD device, the pixel and common electrodes arepositioned on the lower and upper substrates, respectively, and theelectric field induced between the pixel and common electrodes issubstantially perpendicular to the lower and upper substrates. However,these related art LCD devices have a very narrow viewing angle. In orderto solve the problem of narrow viewing angle, in-plane switching liquidcrystal display (IPS-LCD) devices have been proposed. The IPS-LCDdevices typically include a lower substrate in which a pixel electrodeand a common electrode are disposed, an upper substrate having noelectrode, and a liquid crystal interposed between the upper and lowersubstrates. A detailed explanation of a related art IPS-LCD panel willbe provided with reference to FIG. 1.

FIG. 1 is a plan view illustrating an array substrate for use in arelated art IPS-LCD device. As shown in FIG. 1, a plurality of gatelines 14 are disposed in a transverse direction and spaced apart fromeach other by a predetermined distance. A plurality of common lines 18are also disposed parallel to the gate lines 14, and each common line 18is adjacent to each gate line 14. A plurality of data lines 30 aredisposed in a longitudinal direction substantially perpendicular to thegate and data lines 14 and 18. Pairs of the gate and data lines 14 and30 define a pixel region P. A gate pad 16 is disposed at one end of eachgate line 14, and a data pad 40 is disposed at one end of each data line30. Near a crossing of the gate and data lines 14 and 30, a thin filmtransistor T is provided including a gate electrode 12, an active layer26, a source electrode 32, and a drain electrode 34. The gate electrode12 extends from the gate line 14, whereas the source electrode 32extends from the data line 30. The active layer 26 is disposed over thegate electrode 12, and the source and drain electrodes 32 and 34 are incontact with the active layer 26.

In the pixel region P, a plurality of pixel electrodes 38 aresubstantially parallel to the data lines 30. The plurality of pixelelectrodes 38 are electrically connected to the drain electrode 34 ofthe thin film transistor T. A plurality of common electrodes 20 are alsodisposed within the pixel region P and substantially parallel to thedata lines 30. The common electrodes 20 are substantially perpendicularto and connected to the common line 18. The common electrodes 20 arearranged in an alternating pattern with the pixel electrodes 30.

In the pad portions where the gate and data pads 16 and 50 are located,there are provided gate pad electrodes 48 and data pad electrodes 50.The gate pad electrodes 48 contact the gate pads 16, respectively, andthe data pad electrodes 50 contact the data pads 40, respectively.

In the above illustrated array substrate for use in the IPS-LCD panel,the source and drain electrodes 32 and 34 and the data lines 30 areusually single-layered patterns formed of molybdenum (Mo) or chromium(Cr). However, the Mo and Cr metals have a high electrical resistance,the array substrate including the Mo or Cr patterns may not be used foran IPS-LCD panel that requires a large size and an ultra highresolution.

FIGS. 2A-2D, 3A-3D, 4A-4D and 5A-5D are cross sectional views takenalong lines II-II, IV-IV and V-V of FIG. 1, respectively, and illustratethe process of forming the array substrate of FIG. 1 according to arelated art.

In FIGS. 2A, 3A, 4A and 5A, a conductive metallic material, for example,aluminum (Al) or aluminum alloy, is deposited on a substrate 10, andthen patterned using a first mask (not shown), to form a gate electrode12, a gate line 14, a gate pad 16, a common line 18, and a plurality ofcommon electrodes 20. As described with reference to FIG. 1, the gateand common lines 14 and 18 are formed adjacent to and parallel to eachother. The gate electrode 12 extends from the gate line 14, and the gatepad 16 is disposed at one end of the gate line 14. The common electrodes20 perpendicularly extend from the common line 18 in a directionopposite to the adjacent gate line. After patterning the conductivemetallic material, a gate insulating layer 24 is formed over an entiresurface of the substrate 10 to cover all of the gate electrode 12, thegate line 14, the gate pad 16, the common line 18, and the plurality ofcommon electrodes 20.

In FIGS. 2B, 3B, 4B and 5B, pure amorphous silicon (a-Si:H) and dopedamorphous silicon (n+ a-Si:H) are sequentially deposited on the gateinsulating layer 24, and then patterned using a second mask, to form anactive layer 26 and an ohmic contact layer 28 on the gate insulatinglayer 24 in series. Especially, the active and ohmic contact layers 26and 28 are disposed over the gate electrode 12.

Next in FIGS. 2C, 3C, 4C and 5C, a second metallic material (e.g.,chromium or molybdenum) is deposited over the gate insulating layer 24and covers the active and ohmic contact layers 26 and 28. Thereafter,the second metallic material is patterned by a third mask process, toform a data line 30, a source electrode 32 and a drain electrode 34. Thedata line 30 perpendicularly crosses the gate line (reference 14 of FIG.1), and defines a pixel region P. The source electrode 32 extends fromthe data line 30, and contacts the ohmic contact layer 28. The drainelectrode 34 is spaced apart from the source electrode across the gateelectrode 12, and also contacts the ohmic contact layer 28. Whenpatterning the second metallic material in order to form the data line30, a plurality of pixel electrodes 38 are also formed on the gateinsulating layer 38. Each pixel electrode 38 being parallel with thedata line 30 is disposed between the common electrodes 20. Additionally,a gate pad 40 is formed at one end of the gate line 30. After patterningthe second metallic material, a passivation layer 42 is formed over anentire surface of the substrate 10 to cover all of the data line 30, thesource and drain electrodes 32 and 34, the pixel electrodes 38, and thedata pad 40. The passivation layer 42 is silicon oxide (SiO2) or siliconnitride (SiNX). Thereafter, the passivation layer 42 is patterned usinga fourth mask to form a gate pad contact hole 44 and a data pad contacthole 46. The gate pad contact hole 44 exposes a portion of the gate pad16, whereas the data pad contact hole 46 exposes a portion of the datapad 40, as shown in FIGS. 4C and 5C.

In FIGS. 2D, 3D, 4D and 5D, a transparent conductive material, forexample, indium tin oxide (ITO), is deposited on the passivation layer42 and then patterned using a fifth mask. Thus, a gate pad electrode 48contacting the gate pad 16 is formed, and a data pad electrode 50contacting the data pad 40 is also formed.

However, the array substrate fabricated by the above-mentioned processhas some disadvantages. Because the data lines and the source and drainelectrodes are all formed of the metallic material having a lowelectrical resistance, for example, molybdenum (Mo) or chromium (Cr),the array substrate is not adequate in a LCD panel requiring a ultrahigh resolution.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to an array substrate foran in-plane switching mode liquid crystal display LCD device and methodof manufacturing the same that substantially obviates one or more of theproblems due to limitations and disadvantages of the related art.

An advantage of the present invention is to provide an array substrateand a method of forming the array substrate for use in an IPS-LCD devicewhich have a double-layered metallic patterns in order to reduce asignal delay in the lines.

Another advantage of the present invention is to provide a method offorming the array substrate for use in an IPS-LCD device which providesa reduced fabrication process and decreases processing costs.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. These andother advantages of the invention will be realized and attained by thestructure particularly pointed out in the written description and claimshereof as well as the appended drawings.

To achieve these and other advantages, and in accordance with thepurpose of the present invention, as embodied and broadly described, anarray substrate for an in-plane switching liquid crystal display devicecomprising a gate line disposed in a first direction on a substrate; agate electrode extending from the gate line, wherein the gate electrodeand the gate line have a first double-layered structure consisting of afirst barrier layer and a first low resistance metallic layer; a gatepad connected to one end of the gate line; a common line substantiallyparallel and adjacent to the gate line; a data line disposed in a seconddirection and defining a pixel region with the gate line, wherein thedata line has a second double-layered structure consisting of a secondbarrier layer and a second low resistance metallic layer; a data paddisposed at one end of the data line; a plurality of common electrodesextending from the common line to the pixel region and disposed in adirection opposite to the adjacent gate line; a thin film transistordisposed near a crossing of the gate and data lines, the thin filmtransistor including a semiconductor layer, the gate electrode, a sourceelectrode, and a drain electrode, wherein each of the source and drainelectrodes has the same double-layered structure as the data line; and aplurality of pixel electrodes disposed in the direction opposite theadjacent gate lines and connected to the drain electrode, wherein thepixel electrodes are arranged in an alternating pattern with the commonelectrodes.

In another aspect, a method of forming an array substrate for use in anin-plane switching liquid crystal display device is provided. The methodincludes forming a gate line and a gate electrode on a substrate, thegate line being disposed in a first direction and the gate electrodeextending from the gate line, wherein the gate electrode and the gateline have a first double-layered structure consisting of a first barrierlayer and a first low resistance metallic layer; forming a gate padconnected to one end of the gate line; forming a common linesubstantially parallel and adjacent to the gate line; forming a dataline in a second direction, the data line defining a pixel region withthe gate line, wherein the data line has a second double-layeredstructure consisting of a second barrier layer and a second lowresistance metallic layer; forming a data pad at one end of the dataline; forming a plurality of common electrodes in a direction oppositeto an adjacent gate line, the common electrodes extending from thecommon line to the pixel region; forming a thin film transistor near acrossing of the gate and data lines, the thin film transistor includinga semiconductor layer, the gate electrode, a source electrode, and adrain electrode, wherein each of the source and drain electrodes has thesame double-layered structure as the data line; and forming a pluralityof pixel electrodes in the direction opposite the adjacent gate linesand connected to the drain electrode, wherein the pixel electrodes arearranged in an alternating pattern with the common electrodes.

In another aspect, a method of forming an array substrate for use in anin-plane switching liquid crystal display device is provided. The methodincludes sequentially forming a first barrier layer and a first lowresistance metallic layer on a substrate; simultaneously patterning thefirst barrier layer and the first low resistance metallic layer using afirst mask process to form a gate line, a gate electrode, a gate pad anda plurality of common electrodes on the substrate, wherein the gate lineis disposed in a first direction, the gate pad is connected to one endof the gate line, the gate electrode extends from the gate line, and theplurality of common electrodes are disposed in a direction opposite toan adjacent gate line, and wherein the gate electrode and the gate linehave a first double-layered structure consisting of the first barrierlayer and the first low resistance metallic layer; forming a gateinsulating layer over the substrate to cover the gate line, the gateelectrode, the gate pad and the plurality of common electrodes; formingan active layer and an ohmic contact layer on the gate insulating layerusing a second mask, the active layer and the ohmic contact layerdisposed over the gate electrode; sequentially forming a second barrierlayer and a second low resistance metallic layer on the gate insulatinglayer to cover the active and ohmic contact layers; simultaneouslypatterning the second barrier layer and the second low resistancemetallic layer using a third mask to form a data line in a seconddirection, a data pad at one end of the data line, a source electrodeextending from the data line, a drain electrode spaced apart from thesource electrode across the gate electrode, and a plurality of pixelelectrodes in the direction opposite the adjacent gate line and arrangedin an alternating pattern with the common electrodes, wherein the dataline defines a pixel region with the gate line, the pixel electrodes areconnected to the drain electrode, and the data line and the source anddrain electrodes have a second double-layered structure consisting ofthe second barrier layer and the second low resistance metallic layer;forming a passivation layer over the gate insulating layer to cover thedata line, the data pad, the source electrode, the drain electrode, andthe plurality of pixel electrodes; and patterning the passivation layerusing a fourth mask to form a gate pad contact hole and a data padcontact hole, the gate pad contact hole exposing the gate pad and thedata pad contact hole exposing the data pad.

In another aspect, a method of forming an array substrate for anin-plane switching liquid crystal display device is provided. The methodincludes sequentially forming a first barrier layer and a first lowresistance metallic layer on a substrate; simultaneously patterning thefirst barrier layer and the first low resistance metallic layer using afirst mask process to form a gate line, a gate electrode, a gate pad anda plurality of common electrodes on the substrate, wherein the gate lineis disposed in a first direction, the gate pad is connected to one endof the gate line, the gate electrode extends from the gate line, and theplurality of common electrodes are disposed in a direction opposite toan adjacent gate line, and wherein the gate electrode and the gate linehave a first double-layered structure consisting of the first barrierlayer and the first low resistance metallic layer; forming a gateinsulating layer over the substrate to cover the gate line, the gateelectrode, the gate pad and the plurality of common electrodes;sequentially forming a pure amorphous silicon layer, a doped amorphoussilicon layer, a second barrier layer and a second low resistance on thegate insulating layer; simultaneously patterning the pure and dopedamorphous silicon layers and the second barrier and low resistancemetallic layers using a second mask process to form a data line in asecond direction, a data pad at one end of the data line, a sourceelectrode extending from the data line, a drain electrode spaced apartfrom the source electrode across the gate electrode, a plurality ofpixel electrodes in the direction opposite the adjacent gate line andarranged in an alternating pattern with the common electrodes, and aplurality of semiconductor layer under the data line, the data pad, thesource and drain electrodes, and the plurality of pixel electrodes,wherein the semiconductor layer is a double-layered structure consistingof a first layer of pure amorphous silicon and a second layer of dopedamorphous silicon, and wherein the data line defines a pixel region withthe gate line, the pixel electrodes is connected to the drain electrode,and the data line and the source and drain electrodes have a seconddouble-layered structure consisting of the second barrier layer and thesecond low resistance metallic layer; forming a passivation layer overthe gate insulating layer to cover the data line, the data pad, thesource electrode, the drain electrode, the plurality of pixelelectrodes; and patterning the passivation layer using a third maskprocess to form a gate pad contact hole and a data pad contact hole, thegate pad contact hole exposing the gate pad and the data pad contacthole exposing the data pad.

In another aspect, a method of forming an array substrate for anin-plane switching liquid crystal display device is provided. The methodincludes providing first and second substrates; sequentially forming afirst barrier layer and a first low resistance metallic layer on thefirst substrate; simultaneously patterning the first barrier layer andthe first low resistance metallic layer using a first mask process toform a gate line, a gate electrode, a gate pad and a plurality of commonelectrodes on the first substrate, wherein the gate line is disposed ina first direction, the gate pad is connected to one end of the gateline, the gate electrode extends from the gate line, and the pluralityof common electrodes are disposed in a second direction opposite to anadjacent gate line, and wherein the gate electrode and the gate linehave a first double-layered structure consisting of the first barrierlayer and the first low resistance metallic layer; forming a gateinsulating layer over the first substrate to cover the gate line, thegate electrode, the gate pad and the plurality of common electrodes;forming an active layer and an ohmic contact layer on the gateinsulating layer using a second mask, the active layer and the ohmiccontact layer disposed over the gate electrode; sequentially forming asecond barrier layer and a second low resistance metallic layer on thegate insulating layer to cover the active and ohmic contact layers;simultaneously patterning the second barrier layer and the second lowresistance metallic layer using a third mask to form a data line in thesecond direction, a data pad at one end of the data line, a sourceelectrode extending from the data line, a drain electrode spaced apartfrom the source electrode across the gate electrode, and a plurality ofpixel electrodes in the second direction and connected to the drainelectrode, wherein the pixel electrodes are arranged in an alternatingpattern electrodes, wherein the data line defines a pixel region withthe gate line, and the data line and the source and drain electrodeshave a second double-layered structure consisting of the second barrierlayer and the second low resistance metallic layer; forming apassivation layer over the gate insulating layer to cover the data line,the data pad, the source electrode, the drain electrode, and theplurality of pixel electrodes; attaching the second substrate to thefirst substrate using a sealant; cropping peripheral portions of thesecond substrate to expose gate and data portions; and etching a portionof the passivation layer corresponding to the gate and data portions toexpose the gate and data pads.

In another aspect, a method of forming an array substrate for anin-plane switching liquid crystal display device is provided. The methodincludes providing first and second substrates; sequentially forming afirst barrier layer and a first low resistance metallic layer on a firstsubstrate; simultaneously patterning the first barrier layer and thefirst low resistance metallic layer using a first mask process to form agate line, a gate electrode, a gate pad and a plurality of commonelectrodes on the first substrate, wherein the gate line is disposed ina first direction, the gate pad is connected to one end of the gateline, the gate electrode extends from the gate line, and the pluralityof common electrodes are disposed in a second direction opposite to anadjacent gate line, and wherein the gate electrode and the gate linehave a first double-layered structure consisting of the first barrierlayer and the first low resistance metallic layer; forming a gateinsulating layer over the first substrate to cover the gate line, thegate electrode, the gate pad and the plurality of common electrodes;sequentially forming a pure amorphous silicon layer, a doped amorphoussilicon layer, a second barrier layer and a second low resistance on thegate insulating layer; simultaneously patterning the pure and dopedamorphous silicon layers and the second barrier and low resistancemetallic layers using a second mask process to form a data line in thesecond direction, a data pad at one end of the data line, a sourceelectrode extending from the data line, a drain electrode spaced apartfrom the source electrode across the gate electrode, a plurality ofpixel electrodes in the second direction and arranged in an alternatingpattern with the common electrodes, and a plurality of semiconductorlayer under the data line, the data pad, the source and drainelectrodes, and the plurality of pixel electrodes, wherein thesemiconductor layer is a double-layered structure consisting of a firstlayer of pure amorphous silicon and a second layer of doped amorphoussilicon, and wherein the data line defines a pixel region with the gateline, the pixel electrodes are connected to the drain electrode, and thedata line and the source and drain electrodes have a seconddouble-layered structure consisting of the second barrier layer and thesecond low resistance metallic layer; forming a passivation layer overthe gate insulating layer to cover the data line, the data pad, thesource electrode, the drain electrode, and the plurality of pixelelectrodes; attaching the second substrate to the first substrate usinga sealant; cropping peripheral portions of the second substrate toexpose gate and data portions; and etching a portion of the passivationlayer corresponding to the gate and data portions to expose the gate anddata pads.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the presentinvention and together with the description serve to explain theprinciples of that invention.

In the drawings:

FIG. 1 is a plan view illustrating an array substrate for use in arelated art IPS-LCD device;

FIGS. 2A-2D, 3A-3D, 4A-4D and 5A-5D are cross sectional views takenalong lines II-II, III-III, IV-IV and V-V of FIG. 1, respectively, andillustrate the process of forming the array substrate of FIG. 1according to the related art;

FIGS. 6A-6F, 7A-7F, 8A-8F and 9A-9F are cross sectional views takenalong lines VI-VI, VII-VII, VIII-VIII and IX-IX of FIG. 1, respectively,and illustrate the process of forming the array substrate of FIG. 1according to a first embodiment of the present invention;

FIG. 10 is a plan view illustrating an array substrate for use in anIPS-LCD device according to a second embodiment of the presentinvention;

FIGS. 11A-11E, 12A-12E, 13A-13E and 14A-14E are cross sectional viewstaken along lines XI-XI, XII-XII, XIII-XIII and XIV-XIV of FIG. 10,respectively, and illustrate the process of forming the array substrateof FIG. 10;

FIG. 15 is a plan view illustrating an array substrate for use in anIPS-LCD device according to a third embodiment of the present invention;

FIGS. 16A-16H, 17A-17H, 18A-18H and 19A-19H are cross sectional viewstaken along lines XVI-XVI, XVII-XVII, XVIII-XVIII and XIX-XIX of FIG.15, respectively, and illustrate the process of forming the arraysubstrate of FIG. 15; and

FIGS. 20 and 21 are schematic plan views of an IPS-LCD panel andillustrate the process according to a fourth embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Reference will now be made in detail to embodiments of the presentinvention, examples of which are shown in the accompanying drawings.Wherever possible, similar reference numbers will be used throughout thedrawings to refer to the same or similar parts.

FIGS. 6A-6F, 7A-7F, 8A-8F and 9A-9F are cross sectional views takenalong lines VI-VI, VII-VII, VIII-VIII and IX-IX of FIG. 1, respectively,and illustrate the process of forming the array substrate according to afirst embodiment of the present invention. A discussion of elementssimilar to those in FIG. 1 are omitted. In the first embodiment, thearray substrate is fabricated using a five-mask process, and includesdouble-layered metal patterns consisting of a first layer of titanium(Ti) and a second layer of copper (Cu).

In FIGS. 6A, 7A, 8A and 9A, titanium (Ti) and copper (Cu) aresequentially deposited on a substrate 100, to form a first Ti layer 102and a first Cu layer 104 in series. The first Ti layer 102 may have athickness of about 100-150 angstroms (Å) or about 1000 angstroms (Å),and the first Cu layer 104 may have a thickness of about 1500-2000angstroms (Å). The first Ti layer 102 functions as a barrier layer thathelps the first Cu layer 104 to adhere to the substrate 100.Specifically, because the first Cu layer 104 does not adhere well to thesubstrate 100, the first Ti layer 102 compensates and increases theadherence between the substrate 100 and the first Cu layer 104.

In FIGS. 6B, 7B, 8B and 9B, the first Ti layer 102 and the first Culayer 104 are simultaneously patterned using a first mask process toform a gate electrode 106, a gate line 108 and a gate pad 110.Additionally, a common line 112 and a plurality of common electrodes 114are formed. The gate and common lines 108 and 112 are formed adjacent toand substantially parallel to each other. The gate electrode 106 extendsfrom the gate line 108, and the gate pad 110 is disposed at one end ofthe gate line 108. The common electrodes 114 are substantiallyperpendicular to and extend from the common line 112 in a directionopposite to the adjacent gate line.

When patterning the double-layered metal layer of Ti and Cu, a mixedsolution is used. The mixed solution includes hydrogen peroxide (H₂O₂),an etching agent, a solution having fluoride (F), and an additive forcontrolling an etch profile. The etching agent includes SO₄ components(i.e., 2KHSO₅, KHSO₄, K₂SO₄), COOH components (i.e., acetic acid), orPO₄ components. The solution having fluoride (F) is hydrogen fluoride(HF) or ammonium fluoride (NH₄F), for example.

After patterning the Ti and Cu layers 102 and 104, a gate insulatinglayer 116 is formed over an entire surface of the substrate 100 to coverall the first double-layered metal patterns, such as the gate electrode106, the gate line 108, the gate pad 110, the common line 112, and theplurality of common electrodes 114. The gate insulating layer 116 is aninorganic material, for example, silicon nitride (SiN_(x)) or siliconoxide (SiO₂).

Next in FIGS. 6C, 7C, 8C and 9C, pure amorphous silicon (a-Si:H) anddoped amorphous silicon (n+ a-Si:H) are sequentially deposited on thegate insulating layer 116, and then patterned using a second mask. Thus,an active layer 118 and an ohmic contact layer 120 are formed in serieson the gate insulating layer 116. The active and ohmic contact layers118 and 120 are disposed over the gate electrode 106. After that,titanium (Ti) and copper (Cu) are sequentially deposited on the gateinsulating layer 116 to cover the active and ohmic contact layers 118and 120, to form a second Ti layer 122 and a second Cu layer 124.

Now in FIGS. 6D, 7D, 8D and 9D, the second Ti and Cu layers 122 and 124are simultaneously patterned using a third mask to form seconddouble-layered metal patterns, such as a source electrode 126, a drainelectrode 128, a data line 130, a data pad 132, and a plurality of pixelelectrodes 134. The data line 130 is substantially perpendicular to andcrosses the gate and common lines 108 and 112 to define a pixel regionP. The source electrode 126 extends from the data line 130 and contactsthe ohmic contact layer 120. The drain electrode 128 is spaced apartfrom the source electrode 126 across the gate electrode 106, and alsocontacts the ohmic contact layer 120. The data pad 132 is disposed atone end of the data line 130. Each pixel electrode 134 is substantiallyparallel to the data line 130 and disposed between the common electrodes114. The plurality of pixel electrodes 134 are electrically connected tothe drain electrode 128.

As described in FIG. 6D, each of the source and drain electrodes 126 and128 consists of a first layer T.L of titanium (Ti) and a second layerC.L of copper (Cu). The first layer T.L directly contacts the underlyingohmic contact layer 120 so that it prevents the second layer C.L fromdirectly connecting to the ohmic contact layer 120. If the second layerC.L of copper contacts the ohmic contact layer 120 without the firstlayer T.L of titanium, the copper of the second layer C.L reacts withsilicon (Si) of the ohmic contact layer 120 and to produce an interlayerbetween the second layer C.L and the ohmic contact layer 120. Theinterlayer deteriorates and degrades characteristics of the thin filmtransistor. Accordingly, the first layer T.L of titanium prevents thedirect contact between the second layer C.L and the ohmic contact layer120.

After forming the source and drain electrodes 126 and 128 having thedouble-layered metal patterns, a portion of the ohmic contact layer 120exposed between the source and drain electrodes 126 and 128 is removed.Furthermore, a passivation layer 136 is formed over an entire surface ofthe substrate 100 to cover the source and drain electrodes 126 and 128,the data line 130, the data pad 132, and the plurality of pixelelectrodes 134. The passivation layer 136 may be an organic material,for example, benzocyclobutene (BCB) or acrylic resin.

FIGS. 6E, 7E, 8E and 9E illustrate a fourth mask process of forming agate pad contact hole 138 and a data pad contact hole 140. Portions ofthe gate insulating layer 116 and the passivation layer 136 over thegate pad 110 are simultaneously etched, and at the same time a portionof the passivation layer 136 over the data pad 132 is also etched. Thus,a gate pad contact hole 138 and a data pad contact hole 140 are formed,respectively, exposing a portion of the gate pad 110 and a portion ofthe data pad 132. Thereafter, the second layers C.L of the gate and datapads 110 and 132, which are exposed respectively by the gate pad anddata pad contact holes 138 and 140, are removed to expose the underlyingfirst layers T.L of the gate and data pads 110 and 132.

When forming the gate and data pad contact holes 138 and 140, thepassivation layer 136 is removed by a dry etch, and some of the organicmaterial may remain on the surface of the second layer C.L of the gateand data pads 110 and 132. Some of the residual of the organic materialis not removed during a later-conducted washing process, and theresidual increases the contact resistance of the gate and data pads 110and 132 when the outer circuit is connected to the gate and data pads110 and 132. Thus, the second layers C.L exposed by the gate and datapad contact holes 138 and 140 are removed to eliminate the organicresidual of the passivation layer 136 from the gate and data pads 110and 132. The second layers C.L of copper exposed by the gate and datapad contact holes 138 and 140 are etched by a wet etch using a mixedsolution of hydrogen peroxide (H₂O₂) and acetic acid (CH₃COOH).

FIGS. 6F, 7F, 8F and 9F illustrate a fifth mask process of forming agate pad terminal 142 and a data pad terminal 144. A transparentconductive material, for example, indium tin oxide (ITO) or indium zincoxide (IZO), is formed over the passivation layer 136 having the gatepad and data pad contact holes 138 and 140. Then, the transparentconductive material is patterned using a fifth mask process to form thegate pad terminal 142 contacting the first layer T.L of the gate pad110, and the data pad terminal 144 contacting the first layer T.L of thedata pad 132. Accordingly, the array substrate for use in the IPS-LCDdevice is fabricated according to the first embodiment of the presentinvention.

FIG. 10 is a plan view illustrating an array substrate for use in anIPS-LCD device according to a second embodiment of the presentinvention. Unlike the first embodiment, a four-mask process canfabricate the array substrate in the second embodiment.

As shown in FIG. 10, a plurality of gate lines 208 are disposed in atransverse direction and spaced apart from each other by a predetermineddistance. A plurality of common lines 212 are also disposedsubstantially parallel to the gate lines 208, and each common line 212is adjacent to each gate line 208. A plurality of data lines 230 aredisposed in a longitudinal direction substantially perpendicular to thegate and data lines 208 and 212. Pairs of the gate and data lines 208and 230 define a pixel region P. A gate pad 210 is disposed at one endof each gate line 208, and a data pad 232 is disposed at one end of eachdata line 230.

Near a crossing of the gate and data lines 208 and 230, there isprovided a thin film transistor T including a gate electrode 206, anactive layer 218, a source electrode 226, and a drain electrode 228. Thegate electrode 206 extends from the gate line 208, whereas the sourceelectrode 226 extends from the data line 230. The active layer 218 isdisposed over the gate electrode 206, and the source and drainelectrodes 226 and 228 are over the active layer 218.

A plurality of pixel electrodes 234 that are substantially parallel tothe data lines 30 are located in the pixel region P. The plurality ofpixel electrodes 234 are electrically connected to the drain electrode228 of the thin film transistor T. A plurality of common electrodes 214are also disposed within the pixel region P and substantially parallelto the data lines 230. The common electrodes 214 are substantiallyperpendicular and connected to the common line 212. The commonelectrodes 214 are arranged in an alternating pattern with the pixelelectrodes 234.

In the second embodiment shown in FIG. 10, the gate electrode 206, thegate line 208, the source and drain electrodes 226 and 228, and the dataline 230 have a double layered structure of titanium (Ti) and copper(Cu). Because copper (Cu) has a low electrical resistance, the signaldelay may be prevented and the array substrate having thosedouble-layered metal patterns can be used for the IPS-LCD panel having alarge size.

Referring back to FIG. 10, the gate and data pads 210 and 232 also havea double-layered metal structure of Ti and Cu, and the underlying Tilayers T.L are exposed by removing overlying Cu layers, respectively.Thus, the external driving circuits may be connected to the exposed Tilayers T.L in the second embodiment of the present invention.

FIGS. 11A-11E, 12A-12E, 13A-13E and 14A-14E are cross sectional viewstaken along lines XI-XI, XII-XII, XIII-XIII and XIV-XIV of FIG. 10,respectively, and illustrates the process of forming the array substrateof FIG. 10. FIGS. 11A-11E illustrate the process of forming the thinfilm transistor, FIGS. 12A-12E illustrate the process of forming thepixel region, FIGS. 13A-13E illustrate the process of forming the gatepad, and FIGS. 14A-14E illustrate the process of forming the data pad.

In FIGS. 11A, 12A, 13A and 14A, titanium (Ti) and copper (Cu) aresequentially deposited on a substrate 200 to form a first Ti layer 202and a first Cu layer 204 in series. The first Ti layer 202 may have athickness of 150-200 angstroms (Å) or 1000 angstroms (Å), and the firstCu layer 204 may have a thickness of 1500-2000 angstroms (Å). The firstTi layer 202 functions as a barrier layer that helps the first Cu layer204 to adhere to the substrate 200. Specifically, because the first Culayer 204 does not have a good adherence to the substrate 200, the firstTi layer 202 compensates and increases the adherence between thesubstrate 200 and the first Cu layer 204.

In FIGS. 11B, 12B, 13B and 14B, the first Ti layer 202 and the first Culayer 204 are simultaneously patterned using a first mask process, toform a gate electrode 206, a gate line 208 and a gate pad 210. Furtherat this time of patterning, a common line 212 and a plurality of commonelectrodes 214 are also formed. The gate and common lines 208 and 212are disposed adjacent to and substantially parallel to each other. Thegate electrode 206 extends from the gate line 208, and the gate pad 210is disposed at one end of the gate line 208. The common electrodes 214are substantially perpendicular to and extend from the common line 212in a direction opposite to the adjacent gate line.

When patterning the double-layered metal layers of Ti and Cu, a mixedsolution is used. The mixed solution includes hydrogen peroxide (H₂O₂),an etching agent, a solution having fluoride (F), and an additive forcontrolling an etch profile. The etching agent includes SO₄ components(i.e., 2KHSO₅, KHSO₄, K₂SO₄), COOH components (i.e., acetic acid), orPO₄ components. The solution having fluoride (F) is hydrogen fluoride(HF) or ammonium fluoride (NH₄F), for example.

After patterning the Ti and Cu layers 202 and 204, a gate insulatinglayer 216 is formed over an entire surface of the substrate 200 to coverall first double-layered metal patterns, such as the gate electrode 206,the gate line 208, the gate pad 210, the common line 212, and theplurality of common electrodes 214. The gate insulating layer 216 is aninorganic material, for example, silicon nitride (SiN_(X)) or siliconoxide (SiO₂).

Next in FIGS. 11C, 12C, 13C and 14C, pure amorphous silicon (a-Si:H) anddoped amorphous silicon (n+ a-Si:H) are sequentially deposited on thegate insulating layer 216, and then patterned using a second mask. Thus,an active layer 218 and an ohmic contact layer 220 are formed in serieson the gate insulating layer 216. The active and ohmic contact layers218 and 220 are disposed over the gate electrode 206. Next, titanium(Ti) and copper (Cu) are sequentially deposited on the gate insulatinglayer 216 to cover the active and ohmic contact layers 218 and 220 toform a second Ti layer 222 and a second Cu layer 224.

In FIGS. 11D, 12D, 13D and 14D, the second Ti and Cu layers 222 and 224are simultaneously patterned using a third mask to form seconddouble-layered metal patterns, such as a source electrode 226, a drainelectrode 228, a data line 230, a data pad 232, and a plurality of pixelelectrodes 234. The data line 230 perpendicularly crosses the gate andcommon lines 208 and 212 and defines a pixel region P with the gatelines 208. The source electrode 226 extends from the data line 230 andcontacts the ohmic contact layer 220. The drain electrode 228 is spacedapart from the source electrode 226 across the gate electrode 206, andalso contacts the ohmic contact layer 220. The data pad 232 is disposedat one end of the data line 230. Each pixel electrode 234 issubstantially parallel to the data line 230 and disposed between thecommon electrodes 214. The plurality of pixel electrodes 234 areelectrically connected to the drain electrode 228.

As described in FIG. 6D, each of the source and drain electrodes 226 and228 is consists of a first layer of titanium (Ti) and a second layer ofcopper (Cu). The first layer directly contacts the underlying ohmiccontact layer 220 so that it prevents the second layer from directlyconnecting to the ohmic contact layer 220. If the second layer of coppercontacts the ohmic contact layer 220 without the underlying first layerof titanium, the copper of the second layer reacts with silicon (Si) ofthe ohmic contact layer 220 and then produces an interlayertherebetween. The interlayer deteriorates and degrades characteristicsof the thin film transistor. Accordingly, the first layer of titaniumprevents the direct contact between the second layer of copper and theohmic contact layer 220.

Still referring to FIG. 6D, after forming the source and drainelectrodes 226 and 228 having the double-layered metal patterns, aportion of the ohmic contact layer 220 exposed between the source anddrain electrodes 226 and 228 is removed.

Furthermore, a passivation layer 236 is formed over an entire surface ofthe substrate 200 to cover the source and drain electrodes 226 and 228,the data line 230, the data pad 232, and the plurality of pixelelectrodes 234. The passivation layer 236 may be an organic material,for example, benzocyclobutene (BCB) or acrylic resin.

FIGS. 11E, 12E, 13E and 14E illustrate the process of using a fourthmask to form a gate pad contact hole 238 and a data pad contact hole240. Portions of the gate insulating layer 216 and the passivation layer236 over the gate pad 210 are simultaneously etched, and at the sametime a portion of the passivation layer 236 over the data pad 232 isalso etched. Thus, a gate pad contact hole 238 and a data pad contacthole 240 are formed, respectively, exposing a portion of the gate pad210 and a portion of the data pad 232. Thereafter, the second layers C.Lof the gate and data pads 210 and 232, which are exposed respectively bythe gate pad and data pad contact holes 238 and 240, are removed toexpose the underlying first layers T.L of the gate and data pads 210 and232.

As previously described, when forming the gate and data pad contactholes 238 and 240, the passivation layer 236 is removed by a dry etch,and some of the organic material may remain on the surface of the secondlayer C.L of the gate and data pads 210 and 232. A residual of theorganic material is not entirely removed during a later-conductedwashing process. The residual increases the contact resistance of thegate and data pads 210 and 232 and may block the electrical connectionwhen the outer circuit is connected to the gate and data pads 210 and232. Thus, the second layers C.L exposed by the gate and data padcontact holes 238 and 240 are removed to eliminate the organic residualof the passivation layer 236 from the gate and data pads 210 and 232.The second layers C.L of copper exposed by the gate and data pad contactholes 238 and 240 are etched by a wet etch using a mixed solution ofhydrogen peroxide (H₂O₂) and acetic acid (CH₃COOH).

Accordingly with respect to FIGS. 11A-11E, 12A-12E, 13A-13E and 14A-14E,the array substrate for use in the IPS-LCD device is fabricated usingfour-mask processes according to the second embodiment of the presentinvention.

FIG. 15 is a plan view illustrating an array substrate for use in anIPS-LCD device according to a third embodiment of the present invention.In this third embodiment, the array substrate not only includesdouble-layered metal patterns, but also is fabricated using a three-maskprocess.

As shown in FIG. 15, a plurality of gate lines 308 are disposed in atransverse direction and spaced apart from each other by a predetermineddistance. A plurality of common lines 312 are also disposedsubstantially parallel to the gate lines 308, and each common line 312is adjacent to each gate line 308. A plurality of data lines 358 aredisposed in a longitudinal direction substantially perpendicular to thegate and data lines 308 and 312. Pairs of the gate and data lines 308and 358 define a pixel region P. A gate pad 310 is disposed at one endof each gate line 308, and a data pad 360 is disposed at one end of eachdata line 358.

Near a crossing of the gate and data lines 308 and 358, there isprovided a thin film transistor T including a gate electrode 306, anactive layer A.L, a source electrode 354, and a drain electrode 356. Thegate electrode 306 extends from the gate line 308, whereas the sourceelectrode 354 extends from the data line 358. The active layer A.L isdisposed over the gate electrode 306, and the source and drainelectrodes 354 and 356 are over the active layer A.L.

A plurality of pixel electrodes 362 substantially parallel to the datalines 358 are located in the pixel region P. The plurality of pixelelectrodes 362 are electrically connected to the drain electrode 356 ofthe thin film transistor T. A plurality of common electrodes 314 arealso disposed within the pixel region P and substantially parallel tothe data lines 358. The common electrodes 314 are substantiallyperpendicular to and connected to the common line 312. The commonelectrodes 314 are arranged in an alternating pattern with the pixelelectrodes 362.

In the third embodiment illustrated in FIG. 15, the gate electrode 306,the gate line 308, the common line 312 and electrodes 314, the sourceand drain electrodes 354 and 356, the data line 358, and the pixelelectrode 362 each a double layered structure of titanium (Ti) andcopper (Cu). Because copper (Cu) has a low electrical resistance, asignal delay may be prevented and the array substrate having thosedouble-layered metal patterns can be used for the IPS-LCD panel having alarge size.

In FIG. 15, the gate and data pads 310 and 360 also have adouble-layered metal structure of Ti and Cu, and the underlying Tilayers T.L are exposed by way of removing overlying Cu layers,respectively. Thus, the external driving circuits may be connected tothe exposed Ti layers T.L in the gate and data pads 310 and 360 of thethird embodiment of the present invention.

Furthermore, the double-layered metal patterns, such as the source anddrain electrodes 354 and 356, the data line 358, the data pad 360 andthe pixel electrodes 362, are formed with the active layer A.L. Thus,semiconductor layers 342 and 346 are formed underneath thedouble-layered patterns. Such semiconductor layers 342 function toincrease the adhesion of the overlying double-layered metal patterns ofthe source and drain electrodes 354 and 356, the data line 358, the datapad 360 and the pixel electrodes 362.

FIGS. 16A-16H, 17A-17H, 18A-18H and 19A-19H are cross sectional viewstaken along lines XVI-XVI, XVII-XVII, XVIII-XVIII and XIX-XIX of FIG.15, respectively, and illustrate a process of forming the arraysubstrate of FIG. 15. FIGS. 16A-16H show the process of forming the thinfilm transistor, FIGS. 17A-17H show the process of forming the pixelregion, FIGS. 18A-18H show the process of forming the gate pad, andFIGS. 19A-19H show the process of forming the data pad.

In FIGS. 16A, 17A, 18A and 19A, a pixel region P, a switching region S,data regions D, and a data pad region D.L are defined on a substrate300. The pixel region P is an area where the pixel electrode is formed,and the switching region S is an area where the thin film transistor isdefined and disposed at one corner of the pixel region P. The dataregions D are areas where the data lines are formed and are disposed atboth sides of the pixel region P. The data pad region D.L is an areawhere the data pad is formed.

Titanium (Ti) and copper (Cu) are sequentially deposited on an entiresurface of the substrate 300 to form a first Ti layer 302 and a first Culayer 304 in series on the substrate 300. The first Ti layer 302 mayhave a thickness of about 100-200 angstroms (Å), and the first Cu layer304 may have a thickness of about 1500-2000 angstroms (Å). The first Tilayer 302 functions as a barrier layer that helps the first Cu layer 304to strongly adhere to the substrate 300. Specifically, because the firstCu layer 304 does not have good adhesion to the substrate 300, the firstTi layer 302 compensates and increases the adhesion between thesubstrate 300 and the first Cu layer 304.

In FIGS. 16B, 17B, 18B and 19B, the first Ti layer 302 and the first Culayer 304 are simultaneously patterned using a first mask process toform first double-layered metal patterns, such as a gate electrode 306,a gate line 308 and a gate pad 310. Further at this time of patterning,a common line 312 and a plurality of common electrodes 314 are alsoformed in the pixel region P. The common line and common electrodes 312and 314, respectively, also have the double-layered metal structure. Thegate and common lines 308 and 312 are disposed adjacent to andsubstantially parallel to each other. The gate electrode 306 extendsfrom the gate line 308, and the gate pad 310 is disposed at one end ofthe gate line 308. The common electrodes 314 perpendicularly extend fromthe common line 312 in a direction opposite to the adjacent gate line.

After patterning the Ti and Cu layers 302 and 304, a gate insulatinglayer 316 is formed over an entire surface of the substrate 300 to coverall first double-layered metal patterns, such as the gate electrode 306,the gate line 308, the gate pad 310, the common line 312, and theplurality of common electrodes 314. The gate insulating layer 316 is aninorganic material, for example, silicon nitride (SiN_(x)) or siliconoxide (SiO₂). Thereafter, a pure amorphous silicon (a-Si:H) layer 318, adoped amorphous silicon (n+ a-Si:H) 320, a second Ti layer 322, and asecond Cu layer 324 are sequentially deposited on the gate insulatinglayer 316. Then, a photoresist layer 326 is formed on the second Culayer 324.

After forming the photoresist layer 326, a second mask process isconducted. A mask M having first to third portions B1-B3 is disposedover the photoresist layer 326. Light irradiates through the mask M topartially expose the photoresist layer 326. The first portions B1 arelight-shielding areas that completely block the light, the secondportion B2 is a half transmitting area that permits half the light topass, and the third portions B3 are light-transmitting area where thelight thoroughly passes. The first portions B1 correspond to the areaswhere the second double-layered metal patterns are formed, and thesecond portion B2 corresponds to the area where a channel is formed overthe gate electrode 306.

In FIGS. 16C, 17C, 18C and 19C, after the light exposure process usingthe mask M, the photoresist layer 326 is developed to form first tothird photoresist patterns 328, 330 and 332. The first photoresistpattern 328 corresponds in position to the switching region S, and thesecond photoresist patterns 330 correspond in position to the dataregion D and the data pad region D.L. The third photoresist patterns 332are disposed within the pixel region P in positions between the commonelectrodes 314. The first photoresist pattern 328 has an indentedportion 328 a that corresponds to the second portion B2 of the mask.Because half of the light irradiates through the second portion B2during the light exposure process, the indented portion 328 a has aheight half the other portion of the first photoresist pattern 328.

In FIGS. 16D, 17D, 18D and 19D, the pure amorphous silicon layer 318,the doped amorphous silicon layer 320, the second Ti layer 322 and thesecond Cu layer 324 are simultaneously patterned. Specifically, theportions of the second Ti and Cu layers 322 and 324 exposed by the firstto third photoresist patterns 328, 330 and 332 are simultaneouslyremoved using an etching solution, i.e., the wet etching, and the pureand doped amorphous silicon layer 318 and 320 are etched using a dryetch method. Therefore, first to third metal patterns 334, 336 and 338each comprised of Ti—Cu double layers are formed underneath the first tothird photoresist patterns 328, 330 and 332, respectively. Furthermore,first to third silicon patterns 342, 344 and 346 each comprising a firstlayer of pure amorphous silicon and a second layer of doped amorphoussilicon are formed underneath the first to third metal patterns 334, 336and 338, respectively.

As described hereinbefore, when patterning the second Ti and Cu layers322 and 324, a mixed etching solution is used. The mixed solutionincludes hydrogen peroxide (H₂O₂), an etching agent, a solution havingfluoride (F), and an additive for controlling an etch profile. Theetching agent includes SO₄ components (i.e., 2KHSO₅, KHSO₄, K₂SO₄), COOHcomponents (i.e., acetic acid), or PO₄ components. The solution havingfluoride (F) is hydrogen fluoride (HF) or ammonium fluoride (NH₄F), forexample.

FIGS. 16E, 17E, 18E and 19E illustrate a process of ashing the first tothird photoresist patterns 328, 330 and 332. The ashing process isconducted until the indented portion 328a of the first photoresistpattern 328 is completely removed to expose an underlying portion E ofthe first metal pattern 334 corresponding to the gate electrode 306 toform first to third ashed photoresist patterns 348, 350 and 352. Afterthe ashing process, peripheral portions F of the first to third metalpatterns 334, 336 and 338 are exposed because the peripheral portions ofphotoresist patterns are also removed during the ashing process.

In FIGS. 16F, 17F, 18F and 19F, the exposed peripheral portions F of thefirst to third metal patterns 334, 336 and 338 are removed to form asource electrode 354, a drain electrode 356, data lines 358, a data pad360 and a plurality of pixel electrodes 362. Furthermore, the exposedportion E of the first metal pattern 334 is also removed. After that,portions of the doped amorphous silicon layers, which are exposed by theremoval of the exposed portions E and F of the metal patterns 334, 336and 338, are also removed so that the underlying pure amorphous siliconlayers 342(A.S), 344(A.S) and 346(A.S) are exposed in peripheries.Further, the first pure amorphous silicon layer 342(A.S) becomes anactive layer A.L and has a channel between the source and drainelectrodes 354 and 356. The doped amorphous silicon layer on the activelayer 342(A.S) becomes an ohmic contact layer O.L.

Accordingly, the second mask process is complete as described withreference to FIGS. 16B-16F, 17B-17F, 18B-18F and 19B-19F.

In FIGS. 16G, 17G, 18G and 19G, all of the first to third ashedphotoresist patterns 348, 350 and 352 are completely eliminated from theunderlying metal patterns. Thereafter, a passivation layer 364 is formedover an entire surface of the substrate 300 to cover the source anddrain electrodes 354 and 356, the data line 358, the data pad 360, andthe plurality of pixel electrodes 362. The passivation layer 364 may bean organic material, for example, benzocyclobutene (BCB) or acrylicresin.

FIGS. 16H, 17H, 18H and 19H illustrate a process of a third mask offorming a gate pad contact hole 366 and a data pad contact hole 368.Portions of the gate insulating layer 316 and the passivation layer 364over the gate pad 310 are simultaneously etched, and at the same time aportion of the passivation layer 364 over the data pad 360 is alsoetched. Thus, the gate pad contact hole 366 and a data pad contact hole368 are formed, respectively, exposing a portion of the gate pad 310 anda portion of the data pad 360. Thereafter, second layers C.L of the gateand data pads 310 and 360, which are exposed respectively by the gatepad and data pad contact holes 366 and 368, are removed to exposeunderlying first layers T.L of the gate and data pads 310 and 360.

As previously described, when forming the gate and data pad contactholes 366 and 368, the passivation layer 364 are removed by a dry etch,and some of the organic material of the passivation layer 364 may remainon the surface of the second layer C.L of the gate and data pads 310 and360. The residuals of the organic material are not completely removedduring a later-conducted washing process. The residuals increase thecontact resistance of the gate and data pads 310 and 360 and may blockthe electrical connection when the outer circuit is connected to thegate and data pads 310 and 360. Thus, the second layers C.L exposed bythe gate and data pad contact holes 366 and 368 are removed to eliminatethe organic residuals of the passivation layer 326 from the gate anddata pads 310 and 360. The second layers C.L of copper exposed by thegate and data pad contact holes 366 and 368 are etched by a wet etchprocess using a mixed solution of hydrogen peroxide (H₂O₂) and aceticacid (CH₃COOH).

Accordingly, with respect to FIGS. 16A-1614, 17A-17H, 18A-18H and19A-19H, the array substrate for use in the IPS-LCD device is fabricatedusing a three-mask processes according to the third embodiment of thepresent invention. In particular, the first mask process forms the gateline, the gate pad, the gate electrode, the common line and the commonelectrodes, and the second mask process forms the active layer, thesource and drain electrodes, the data line, the data pad, and the pixelelectrodes. Finally, the third mask process forms the gate and data padcontact holes that expose the gate and data pads.

In the second and third embodiments, the final mask processes etch thepassivation layer and the gate insulating layer to expose the gate anddata pads. However, if the gate and data pads are exposed without themask process, the array substrates of the second and third embodimentswill be fabricated using the three- and two-mask processes,respectively. The pad exposing process, which does not use a mask, willbe explained in detail with reference to FIGS. 20 and 21.

FIGS. 20 and 21 are schematic plan views of an IPS-LCD panel andillustrate a fourth embodiment of the present invention.

FIG. 20 shows the IPS-LCD panel after the third mask process of thesecond embodiment or after the second mask process of the thirdembodiment. FIG. 21 is a schematic plan view after exposing the gate anddata pads according to the fourth embodiment of the present invention.

As shown in FIG. 20, the IPS-LCD panel 400 includes a first substrate410 and a second substrate 450 with a liquid crystal layer (not shown)interposed therebetween. The first substrate 410 is the array substrateincluding the double-layered metal patterns. The first substrate 410 isfabricated using the mask processes described above without a final maskprocess of forming the pad contact holes. The second substrate 450 is acolor filter substrate in which a plurality of color filters aredisposed. The first and second substrates 410 and 450 are aligned andattached to each other by a sealant 500. After attaching, the peripheralportions of the second substrate 450 are cut and cropped to expose agate pad portion G.P and a data pad portion D.P of the lower substrate410. A plurality of gate pads 416 having a first layer T.L of titaniumand a second layer C.L of copper are located in the gate pad portionG.P, and a plurality of data pads 414 having a first layer T.L oftitanium and a second layer C.L of copper are located in the data padportion D.P. The lower substrate 410 still includes a passivation layerover the gate and data pad portions G.P and D.P that covers the gate anddata pads 416 and 414.

In FIG. 21, the passivation layer in the gate and data portions G.P. andD.P is removed to expose the gate and data pads 416 and 414. Thereafter,the copper layer C.L of each of the gate and data pads 416 and 414 isremoved using a wet etch method to expose the underlying Ti layer T.L.Accordingly, the array substrate can be fabricated using the three-maskprocess or the two-mask process.

The present invention has the following advantages. First, because ametallic material having a low electrical resistance, for example,copper (Cu), is used for the array lines, the array substrate can beemployed in the large IPS-LCD device requiring a high resolution.

Second, because the copper layers of the Ti/Cu double-layered gate anddata pads are removed, the residuals of organic material remaining onthe copper layer during the patterning process of the organicpassivation layer can be completely removed. Thus, a signal interruptionor blocking caused in the gate and data pads can be prevented. Tantatum(Ta) or Tungsten (W) may be used in place of the Ti layer, and silver(Ag) or platinum (Pt) may be used in place of the Cu layer.

Third, because the array substrate can be fabricated using a four-,three- or two-mask process, it is possible to decrease and simplify theprocess steps. Therefore, the fabrication time and the production costwill be reduced.

It will be apparent to those skilled in the art that variousmodifications and variation can be made in the present invention withoutdeparting from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1-50. (canceled)
 51. A method of forming an array substrate for use inan in-plane switching liquid crystal display device, comprising:providing first and second substrates; sequentially forming a firstbarrier layer and a first low resistance metallic layer on the firstsubstrate; simultaneously patterning the first barrier layer and thefirst low resistance metallic layer using a first mask process to form agate line, a gate electrode, a gate pad and a plurality of commonelectrodes on the first substrate, wherein the gate line is disposed ina first direction, the gate pad is connected to one end of the gateline, the gate electrode extends from the gate line, and the pluralityof common electrodes are disposed in a second direction perpendicular toan adjacent gate line, and wherein the gate electrode and the gate linehave a first double-layered structure consisting of the first barrierlayer and the first low resistance metallic layer; forming a gateinsulating layer over the first substrate to cover the gate line, thegate electrode, the gate pad and the plurality of common electrodes;forming an active layer and an ohmic contact layer on the gateinsulating layer using a second mask, the active layer and the ohmiccontact layer disposed over the gate electrode; sequentially forming asecond barrier layer and a second low resistance metallic layer on thegate insulating layer to cover the active and ohmic contact layers;simultaneously patterning the second barrier layer and the second lowresistance metallic layer using a third mask to form a data line in thesecond direction, a data pad at one end of the data line, a sourceelectrode extending from the data line, a drain electrode spaced apartfrom the source electrode across the gate electrode, and a plurality ofpixel electrodes in the second direction and connected to the drainelectrode, wherein the pixel electrodes are arranged in an alternatingpattern with the common electrodes, wherein the data line defines apixel region with the gate line, and the data line and the source anddrain electrodes have a second double-layered structure consisting ofthe second barrier layer and the second low resistance metallic layer;forming a passivation layer over the gate insulating layer to cover thedata line, the data pad, the source electrode, the drain electrode, andthe plurality of pixel electrodes; attaching the second substrate to thefirst substrate using a sealant; cropping peripheral portions of thesecond substrate to expose gate and data portions; and etching a portionof the passivation layer corresponding to the gate and data portions toexpose the gate and data pads.
 52. The method according to claim 51,wherein the pixel electrodes have the same double-layered structure asthe data line, the common electrodes have the same double-layeredstructure as the gate line, the first mask process forms a common linesubstantially parallel and adjacent to the gate line, the commonelectrodes extend from the common line to the pixel region, the commonline has the same double-layered structure as the gate line and isspaced apart from the gate line, and wherein the gate pad has the samedouble-layered structure as the gate line, and the data pad has the samedouble-layered structure as the data line.
 53. The method according toclaim 51, further comprising removing the first low resistance metalliclayer of the gate pad so that the gate pad has a single -layeredstructure of the first barrier layer.
 54. The method according to claim51, further comprising removing the second low resistance metallic layerof the data pad so that the data pad has a single-layered structure ofthe second barrier layer.
 55. A method of forming an array substrate foruse in an in-plane switching liquid crystal display device, comprising:providing first and second substrates; sequentially forming a firstbarrier layer and a first low resistance metallic layer on a firstsubstrate; simultaneously patterning the first barrier layer and thefirst low resistance metallic layer using a first mask process to form agate line, a gate electrode, a gate pad and a plurality of commonelectrodes on the first substrate, wherein the gate line is disposed ina first direction, the gate pad is connected to one end of the gateline, the gate electrode extends from the gate line, and the pluralityof common electrodes are disposed in a second direction perpendicular toan adjacent gate line, and wherein the gate electrode and the gate linehave a first double-layered structure consisting of the first barrierlayer and the first low resistance metallic layer; forming a gateinsulating layer over the first substrate to cover the gate line, thegate electrode, the gate pad and the plurality of common electrodes;sequentially forming a pure amorphous silicon layer, a doped amorphoussilicon layer, a second barrier layer and a second low resistance on thegate insulating layer; simultaneously patterning the pure and dopedamorphous silicon layers and the second barrier and low resistancemetallic layers using a second mask process to form a data line in thesecond direction, a data pad at one end of the data line, a sourceelectrode extending from the data line, a drain electrode spaced apartfrom the source electrode across the gate electrode, a plurality ofpixel electrodes in the second direction and arranged in an alternatingpattern with the common electrodes, and a plurality of semiconductorlayer under the data line, the data pad, the source and drainelectrodes, and the plurality of pixel electrodes, wherein thesemiconductor layer is a double-layered structure consisting of a firstlayer of pure amorphous silicon and a second layer of doped amorphoussilicon, and wherein the data line defines a pixel region with the gateline, the pixel electrodes are connected to the drain electrode, and thedata line and the source and drain electrodes have a seconddouble-layered structure consisting of the second barrier layer and thesecond low resistance metallic layer; forming a passivation layer overthe gate insulating layer to cover the data line, the data pad, thesource electrode, the drain electrode, and the plurality of pixelelectrodes; attaching the second substrate to the first substrate usinga sealant; cropping peripheral portions of the second substrate toexpose gate and data portions; and etching a portion of the passivationlayer corresponding to the gate and data portions to expose the gate anddata pads.
 56. The method according to claim 55, wherein the pixelelectrodes have the same double-layered structure as the data line, thecommon electrodes have the same double-layered structure as the gateline, the first mask process forms a common line substantially paralleland adjacent to the gate line, the common electrodes extend from thecommon line to the pixel region, the common line has the samedouble-layered structure as the gate line and is spaced apart from thegate line, the gate pad has the same double-layered structure as thegate line, and the data pad has the same double-layered structure as thedata line.
 57. The method according to claim 55, further comprisingremoving the first low resistance metallic layer of the gate pad so thatthe gate pad has a single -layered structure of the first barrier layer.58. The method according to claim 55, further comprising removing thesecond low resistance metallic layer of the data pad so that the datapad has a single-layered structure of the second barrier layer.
 59. Themethod according to claim 55, wherein patterning the first barrier layerand the first low resistance metallic layer and patterning the secondbarrier layer and the second low resistance metallic layer use a mixedetching solution including hydrogen peroxide (H₂O₂), an etching agent, asolution having fluoride (F), and an additive for controlling an etchprofile.
 60. The method according to claim 55, wherein the second maskprocess includes: forming a photoresist layer on the second lowresistance metallic layer; providing a mask over the photoresist layer,the photoresist having a light-shielding portion, a light-transmittingportion, and a half transmitting portion; irradiating light on thephotoresist layer through the mask; developing the photoresist layerexposed by the light to form a first photoresist pattern in a positioncorresponding to the source and drain electrodes, a second photoresistpattern in a position corresponding to the data pad and the data line,and a third photoresist pattern in a position corresponding to the pixelelectrode, wherein the first photoresist pattern has a first and asecond thickness; removing portions of the second low resistancemetallic layer, the barrier layer, the doped amorphous silicon layer andthe pure amorphous silicon layer, which are exposed among the first tothird photoresist patterns; and ashing the first to third photoresistpatterns until a portion having the first thickness is completelyremoved and then removing exposed portions of the second low resistancemetallic layer, the barrier layer and the doped amorphous silicon layeruntil portions of the amorphous silicon layer are exposed.